1. Field of the Invention
The present invention relates to a zoom lens system and an electronic image pickup apparatus using the zoom lens system.
2. Description of the Related Art
In recent years, instead of a silver halide film camera, a digital camera has been a mainstream which photographs a subject by use of an electronic image pickup device such as a CCD image sensor or a CMOS type image sensor. Furthermore, the camera has a large number of categories in a broad range from a highly functional type for business to a compact popular type. A user of the popular type of digital camera would like to readily enjoy photographing in various scenes anywhere and anytime. Therefore, the user would like a small-sized camera, especially a digital camera of a thin type which is conveniently carried with a good storage property in clothing, a bag pocket or the like and which has a small size in a thickness direction.
On the other hand, a zoom ratio of the digital camera of the compact type has been generally about three, but there is a demand for a camera having a higher zoom ratio. As a zoom lens system which easily retains a comparatively high zoom ratio, a type is known which has, in order from an object side, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit having a positive refractive power and a fourth lens unit having a positive refractive power.
Moreover, since a size of the camera in a thickness direction is mainly determined by a size of a lens barrel, thinning of the lens barrel is effective in order to achieve the thinned camera.
In recent years, a so-called collapsible lens barrel of the camera has been generalized which is projected from a camera body when used and which is stored in the camera body when carried. Therefore, there is a demand for the zoom lens system in which the thinning of the lens barrel when collapsed is considered. In, for example, Japanese Patent Application Laid-Open Nos. 2004-258,240, 2004-199,000, 2001-133,687 and 11-119,100, a zoom lens system is disclosed in which a second lens unit includes two lenses of a negative lens and a positive lens, so that the size of the second lens unit in the thickness direction is reduced.